The invention relates to high sensitivity low noise ion detectors for mass spectrometry. In particular, the invention relates to an ion detector having a selective coating for absorbing photon and neutral particles.
Electron multipliers are used in a mass spectrometer to detect the signal, in the form of a beam of positive or negative ions, exiting a mass filter. It is known that light photons, especially those in the ultraviolet region of the electromagnetic spectrum, and neutral particles are primary sources of noise. The electron multiplier amplifies the incoming signal and, in addition, amplifies noise components.
A complete detector assembly usually consists of an electron multiplier and metal hardware to which electrostatic potentials are applied for the purpose of steering and focusing the ion beam. The Noise Figure (NF) of a detector is defined as follows: ##EQU1## Where: S.sub.in =Signal In
S.sub.out =Signal Out PA1 N.sub.in =Noise In PA1 N.sub.out =Noise Out. The Noise Figure can be improved by reducing the noise or increasing the signal that reaches the electron multiplier.